A working machine equipped with an internal combustion engine as a power source typically includes a choke-valve open/close mechanism for opening and closing a choke valve of an intake system of the engine, a throttle-valve open/close mechanism for opening and closing a throttle valve of the intake system, an interlock mechanism for interlocking the choke-valve open/close mechanism and the throttle-valve open/close mechanism, and a release mechanism for releasing the interlock mechanism. For starting the internal combustion engine, an electric switch is moved from a stop position to a start position to electrically turn on an ignition unit. Additionally, if the internal combustion engine is cold, the engine is started after activating the choke-valve open/close mechanism to close the choke valve. In this operation, the choke-valve open/close mechanism is interlocked with the throttle-valve open/close mechanism by the interlock mechanism to allow the throttle valve to be partially opened for the operation-period of the choke-valve open/close mechanism.
For example, Japanese Patent Laid-open Publication No. 5-214972 discloses a chain saw, as a working machine, having a single operation unit for switching between stop, start and choke operations of an internal combustion engine. In the working machine, the operation unit is provided at the front end portion of a handle extending in the lengthwise direction of the body of the working machine. Further, a choke-valve open/close mechanism, a throttle-valve open/close mechanism and an interlock mechanism therefor are housed in an interior space of the rear end portion of the handle. These mechanisms are operationally coupled with the operation unit through a link mechanism to transmit the movement of the operation unit to the mechanisms provided at the rear end portion.
This working machine is highly advantageous in that the stop, start and choke operations of the internal combustion engine can be switched only by a single operation unit. However, the link mechanism provided inside the working machine has a complicated structure, resulting in an increased number of components, deteriorated workability during the assembly process and increased cost.